1. Field of the Invention
The present embodiments relate to plasma processing systems, and in particular, to plasma processing systems that utilize direct current (DC) pulsing as the power source.
2. Description of the Related Art
Plasma has long been employed to process substrates (e. g., semiconductor wafers, flat panels, etc.) to form electronic products (e.g., integrated circuits, flat panel displays, etc.). Semiconductor wafers are typically placed in an etch chamber with a photoresist mask layer to selectively etch the underlying materials. The etching process removes the underlying materials (metals and/or dielectrics) not covered by the photoresist. The etching process, along with other processing operations, is repeated many times for each semiconductor wafer until the end product circuits or devices are formed.
Typically, a plasma etching tool is used to perform the etching process. A plasma etching tool is defined by a chamber that includes a substrate support and a plasma volume over the substrate support. Radio frequency (RF) power is commonly provided to one or more electrodes of the chamber. The electrode configuration can take on various forms, depending on the etch process. Commonly, plasma etching tools used to etch dielectric materials are referred to as capacitive coupled plasma (CCP) tools, and plasma etching tools used to etch conductive materials are referred to as inductive coupled plasma (ICP) tools. No matter the type of tool, both the CCP tools and ICP tools require at least one RF power supply. A RF power supply is typically configured to generate RF signals that are propagated to an electrode of the plasma etching tool via a match circuit and transmission line.
As the demand for higher aspect ratio etching and smaller sizes continues to increase, processing engineers have discovered certain benefits from pulsing the RF power supplied to the electrode of the plasma etching tool. Although pulsing of the RF power supply has shown improvement in the resulting process, pulsing RF power supplies does add complexity and cost. By way of example, pulsing RF power requires precise control of the pulsing sequence, timing, voltage levels, reflection, etc., and such control needs to be continually monitored. Additionally, supplying RF power via a match circuit and transmission line requires the implementation of significant hardware, e.g., such as large discrete capacitors and inductors, and sophisticated transmission lines that include a RF return path.
It is in this context that embodiments arise.